The present invention relates to an ultrasonic inspection apparatus for generating an ultrasound image to be used for inspection or diagnosis of an inspection target by imaging an inspection target such as organ in a living body by transmitting and receiving an ultrasonic beam.
An ultrasonic inspection apparatus using an ultrasound image such as an ultrasound diagnostic apparatus has hitherto been put into practical use in the field of medicine. In general, this kind of ultrasonic inspection apparatus has an ultrasound probe in which a plurality of elements (transducers) is installed, and an apparatus body connected to the ultrasound probe. In the ultrasonic inspection apparatus, an ultrasonic beam is transmitted from the plurality of elements of the ultrasound probe toward an inspection target (subject), an ultrasonic echo from the subject is received by the ultrasound probe, and a signal of the received ultrasonic echo is electrically processed in the apparatus body to generate an ultrasound image.
In an ultrasonic inspection apparatus, when an ultrasound image is generated, the ultrasonic beam is transmitted from the plurality of elements of the probe to an inspection target region of the subject, such as an organ in a living body or a lesion of the organ in a state of being focused thereon, and the ultrasonic echo from a reflector of the inspection target region such as a surface or an interface of the organ or the lesion is received through the plurality of elements. At this time, since ultrasonic echoes reflected by the same reflector are received by the plurality of elements, compared with an ultrasonic echo signal obtained by transmitting an ultrasonic beam from a transmission element and receiving an ultrasonic echo from a reflector located in a focal position of the ultrasonic beam transmitted with the transmission element, an ultrasonic echo signal obtained by receiving an ultrasonic echo reflected by the same reflector with another element different from the transmission element is delayed. Therefore, after an analog/digital (A/D) conversion is performed on the ultrasonic echo signals received by the plurality of elements to obtain element data, reception focus processing, that is, delay correction, phase matching, and phasing addition are performed on the element data to generate a sound ray signal, and an ultrasound image is generated based on the sound ray signal obtained in this way.
In the ultrasonic inspection technology, when the inspection target region of the subject is large, a large number of transmission ultrasonic beams are necessary, and the time required for image generation becomes long. Therefore, in order to improve the conventional technology in which the resolution of an ultrasound image generated depends on the width of the transmission ultrasonic beam, JP 2003-180688 A (Patent document 1) discloses a technology in which an ultrasound image is generated by using a system for generating an ultrasonic beam having a large width and an algorithm for converting a reception ultrasonic echo into image information.
In Patent document 1, first, an ultrasonic beam that is wider than a normal ultrasonic beam (see FIG. 12B in Patent document 1) is designed and transmitted and reception data is obtained (see FIG. 4 therein). In Patent document 1, a polar coordinate (radius R and angle θ) is assigned to a wide beam, and an ultrasound image is generated based on the relationship between the reception data and the geometric coordinate. In the ultrasound image generated in this way, the frame rate of the image increases in comparison with the conventional technology, and the resolution of the image can be improved with respect to the image forming time.
Further, JP 2011-011045 A (Patent document 2) discloses an ultrasound diagnostic apparatus in which a wide ultrasonic beam covering an area of a tissue of a subject is transmitted from a plurality of elements (ultrasound transducers) while performing element shifting of more than one element; parallel raw data (element data) including information of the area of the tissue generated based on a plurality of reception signals due to the ultrasonic echo from the area of the tissue is converted into serial raw data; reception focus processing is performed on the converted raw data to generate an image signal (sound ray signal); and an ultrasound image is generated based on the obtained sound ray signal.
Patent document 2 discloses that when the sound ray signal is generated, one sound ray signal can be generated by transmitting the ultrasonic beam so that two adjacent areas overlap each other and performing signal processing (for example, reception focus processing) using the raw data (element data) obtained through a plurality of transmissions on one sampling point in the overlapped area, thereby a resolution which is degraded due to a widened SN ratio or aperture can be improved. Patent document 2 also discloses that one sound ray signal of which a resolution which is degraded due to the widened SN ratio or aperture is improved can be obtained by generating a plurality of sound ray signals for one sampling point based on the raw data obtained through the plurality of transmissions, and then obtaining an average value of the sound ray signals.
JP 2009-240700 A (Patent document 3) discloses an ultrasound diagnostic apparatus in which transmission ultrasonic waves emitted from a plurality of vibrator constituting a vibrator group for transmission are focused on a transmission focusing point to form a virtual point sound source; reception ultrasonic waves reflected from a plurality of continuous observation points due to the transmission ultrasonic waves emitted from the point sound source are received by a plurality of vibrators constituting a vibrator group for reception; reception phasing addition is performed on each of the reception signals of the channels obtained so that the observation point forms a reception focusing point; further, the same reception phasing addition is performed on the reception signal obtained using each of the vibrator group for reception and the vibrator group for transmission sequentially shifted in an arrangement direction of the vibrator; and transmission phasing addition of correcting a transmission delay caused by a difference in a propagation distance from each transmission focusing point to the observation point on the reception signal after the reception phasing addition.
In Patent document 3, a transmission beam and a reception beam having a narrow beam width that is approximately uniform in a depth direction of a subject can be formed with high precision and high sensitivity by performing the reception phasing addition and the transmission phasing addition on the reception signals obtained from the plurality of vibrators. Accordingly, Patent document 3 discloses that image data having excellent spatial resolution, contrast resolution and S/N can be generated and displayed.